Fix undeclared variable in d8 debugger.

src/d8.js

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2156 matching lines @@
           maxdigits = 3;
         }
         var result = '';
         for (var num = 0; num < lines.length; num++) {
           // Check if there's an extra newline at the end.
           if (num == (lines.length - 1) && lines[num].length == 0) {
             break;
           }
 
           var current_line = from_line + num;
-          spacer = maxdigits - (1 + Math.floor(log10(current_line)));
+          var spacer = maxdigits - (1 + Math.floor(log10(current_line)));
           if (current_line == Debug.State.currentSourceLine + 1) {
             for (var i = 0; i < maxdigits; i++) {
               result += '>';
             }
             result += '  ';
           } else {
             for (var i = 0; i < spacer; i++) {
               result += ' ';
             }
             result += current_line + ': ';
@@ skipping 616 matching lines @@
       json += NumberToJSON_(elem);
     } else if (typeof(elem) === 'string')  {
       json += StringToJSON_(elem);
     } else {
       json += elem;
     }
   }
   json += ']';
   return json;
 }